effect of *pretty-print* on compile-times

[Nikodemus Siivola]

From #lisp, talking about quicklisp:

<Xach> whee, builds just got 1000 seconds faster by setting *print-pretty* to nil.
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<Xach> 4500 to 3500, actually.
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<nikodemus> is that on sbcl, or all platforms?
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<Xach> SBCL

I find this surprising. Maybe it's unavoidable, but should be tracked down anyways.

[Douglas Katzman (dougk)]

The pretty-printer has gotten hugely faster since this bug was opened.
I measured somewhere around 5x faster for forms involving backquote, which now prints in a single pass instead of multiple passes for various different reasons.
(Not counting a pre-pass for circularity detection if applicable, and general pretty-printer overhead such as buffering/queuing)

The speedup is based on not having to reverse-engineer forms like (SB-IMPL::BACKQ-LIST 'X Y) into `(X ,Y), so we save significantly on consing. Additionally, printing a comma no longer requires an evil hack that printed into a string-stream first to decide whether the material under control of the comma would cause a non-splicing comma to accidentally look like splicing-comma, as could happen with a symbol whose name begins with dot or at-sign.

So despite it being a little concerning that the compiler was doing so much output that this actually mattered, I'm marking "fixed"